WRC 568 Current Concepts for Life Assessment of Pressure Vessels and Piping

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WRC 568Title                  Current Concepts for Life Assessment of Pressure Vessels and Piping               
Publication Date                    2016               
Authors                    M. Prager, Ph.D. D.A. Osage, P.E.               
Publication Type                    Bulletin               
Number of Pages                    200               
AbstractThere is no more important subject for study and sharing of experiences and data today than matters relevant to assessing the safety of equipment operating in high-temperature and/or aggressive environments such as in refineries and process plants. The papers collected for WRC Bulletin 568 cover recent very practical advances in the understanding of mechanisms and rates of degradation relevant to a wide range of process equipment. The mechanisms reported are particularly relevant to damage incurred due to the combined effects of elevated-temperature and hydrogen. The technology included in the papers in this Bulletin provide important justification and principles to strengthen the foundation of the Fitness-For-Services rules found in the API-579 and ASME FFS-1. These papers were prepared to be presented at ESOPE 2016 because of the significance of the technical progress reported.
The studies, conclusions and recommendations documented in this WRC Bulletin were the result of focused efforts to strengthen technology relevant to design and life assessment of components for fatigue and environmental damage in high-pressure hydrogen and low-density polyethylene service. The paper FATIGUE ASSESSMENT FOR IN-SERVICE COMPONENTS – A NEW PART FOR API 579-1/ASME FFS-1 FITNESS-FOR-SERVICE addresses technology to be included in a new section of the Joint API ASME document. It includes advanced methods for fatigue assessment of welded joints which will impact additional life assessment and design documents. Similarly, the paper API 579-1/ASME FFS-1 METHODOLOGY FOR EVALUATING THE FITNESS-FOR-SERVICE OF LDPE REACTORS pertains directly to low density polyethylene service (LDPE) but provides methodology which is more broadly applicable.
The paper IMPROVED VALIDATION OF WELDING PROCEDURES FOR PRESSURE VESSELS AND PIPING INTENDED FOR SERVICE TEMPERATURES IN THE CREEP RANGE explains and demonstrates the importance of specimen size and test temperature on the duration of welding procedure qualification tests and provides a basis for guidelines and recommendations for selecting the temperatures and stresses used for those tests. Important recommendations regarding post-test evaluation of test specimens are provided.
EXTENSION OF THE OMEGA METHOD MATERIAL PROPERTIES FOR DESIGN AND LIFE ASSESSMENT explains equations characterizing the stress and temperature dependent properties to be used in the calculations that are found in the Fitness-For-Service Standard maintained jointly by API and ASME as noted above. To deal with modern design concepts and the needs of designers the original equations now need to be extended to cover wider ranges of stresses and temperatures and the variations in material properties due to heat treatment and composition in the specifications covered. The concepts and methods used to extend the respective equations for the alloys covered are presented and explained in this paper.
AN APPROACH TO CREEP-FATIGUE INTERACTION IN PRESSURE VESSELS AND PIPING WHEN DESIGNING WELDED COMPONENTS INCORPORATING CREEP STRENGTH ENHANCED FERRITIC STEELS addresses creep-fatigue damage using a creep/cyclic strain softening model validated using test data characterizing creep strength enhanced ferritic alloys behavior. The model is shown to produce conservative designs. The procedure explicitly considers the effects of stress relaxation, stress/strain redistribution, and the associated creep damage. The equations for creep life estimation are consistent with time-dependent properties used to establish allowable stresses found in ASME Section VIII-2.
Environmental effects, especially associated with hydrogen are extremely important in modern process plants. WRC Bulletin 568 presents three important and practical papers concerning this topic. First, PROGRESS IN ASSESSING THE SAFETY OF C-1/2 MO EQUIPMENT IN LONG TERM ELEVATED TEMPERATURE HYDROGEN PRESSURE VESSEL AND PIPING SERVICE provides insight into metallurgical reasons for the variability in performance of the C-0.5% Mo alloy, including the effects of composition and heat treatment on toughness and hydrogen attack resistance. It is shown that the degree of attack can be correlated with the reduction in Charpy V-notch toughness at positions through the wall of the component. This knowledge can be an effective tool for assessing the safety of operating petroleum refinery equipment. Studies of ex-service materials enabled development of “Toughness Prediction Factors” for the alloy.
THE E2G MODEL OF HIGH TEMPERATURE HYDROGEN ATTACK (HTHA) AND THE NEW PRAGER CURVES offers technical justification for new time-dependent HTHA curves based on proposed models including crack growth and detailed damage rules. The behavior is correlated with multiple time-dependent curves. Probability of failure based on Monte Carlo treatment of variables is demonstrated. This mechanistic basis is presented with examples of its application to Fitness-For-Service problems.
The final paper in this volume, PROPERTIES AND MICROSTRUCTURAL CHANGES ASSOCIATED WITH LONG TERM SERVICE OF PRESSURE VESSEL AND PIPING STEELS AT ELEVATED TEMPERATURES AND IN HYDROGEN AND THEIR DETECTION AND EFFECTS ON REMAINING LIFE presents some of the extensive work of Professor Carl Lundin’s team at the University of Tennessee in characterizing susceptibility of alloys to hydrogen attack. They show that some changes to the service temperature and stress conditions may lead to sudden and unexpected failures. They note that nondestructive test methods, including ultrasonic testing, are often inadequate for detection and characterization of the rate of hydrogen attack damage progression. Recent experience regarding the capabilities of inspection methods and personnel for detection of damage and determination of remaining life are discussed.